I've noticed a fair few items that leave arms, hands, feet, etc still visible behind them.

I'm assuming there's some sort of masking item to cover pieces? Could anyone help me with the name of such items?

You can toggle them off in the Base tab of the wardrobe c:

Ah! I was so convinced it was an item I totally skipped over that section of the wardrobe.

Thank you!

you're welcome!

There are also items, e.g. in the Millionaire Center but they leave a white space so unless you have a niche need for one of those it's probably easier to toggle the limbs off